1. Field of the Invention
This invention relates to primary electrochemical cells having an aqueous electrolyte and a cathode capable of intercalating the anode metal ions.
2. Description of the Prior Art
Alkaline earth metal anodes and aluminum anodes, when employed in electrochemical cells having an aqueous electrolyte at a pH close to neutrality, react very slowly due to a strong passivation layer or film which is formed on the anode surface. This film prevents the electrolyte from reacting with the anode to continue cell operation. It is therefore common practice to saturate an electrolyte solution with lithium chromate which acts as an inhibitor of the formation of the passivation film. The oxidizing effect of lithium chromate provides a film on the anode metal of sufficient porosity to maintain the electrolyte penetration to the anode metal and therefore cell performance is not inhibited by the formation of the usual passivation film on the anode. In U.S. Pat. No. 3,928,076 to Moser, the addition of lithium chloride to an aqueous electrolyte is disclosed as a means of inhibiting the formation of a passivation film or layer on a magnesium anode in contact with an aqueous electrolyte.
Various nonaqueous electrolyte electrochemical cells are disclosed in the prior art having cathodes which are capable of intercalation of an ionized form of the anode metal. U.S. Pat. No. 4,366,215, Coetzer et al, is representative. The insertion of alkali or alkaline earth metal ions into the cathode structure is disclosed in column 12.
There is no suggestion in the prior art that electrochemical cells having aqueous electrolytes and an alkaline earth metal anode will provide a high energy density/high rate primary battery wherein the alkaline earth metal ion of the anode intercalates the cathode structure during the electrochemical reaction to produce an electric current.
It is an object of the invention to provide a high rate, high energy density alkaline earth metal primary electrochemical cell comparable in energy and power density with the lithium/thionylchloride primary cells currently in use. The prior art lithium/thionylchloride cells have excellent energy and power densities but such cells exhibit severe toxicity hazards associated with handling the cells because of the hazardous electrolyte.
Another object of the invention is to provide a process for producing electric current in a high rate, high energy density alkaline earth metal primary cell which overcomes the severe handling and toxicity problems associated with the lithium/thionylchloride electrolyte primary cells of the prior art. The lithium/thionylchloride primary cells currently in use are relatively capacity limited because this cell couples its electrochemistry with a liquid cathode (thionylchloride).